What does success mean to you?

There are many things you can say. This type of question doesn't have a wrong answer. All answers will be correct. So the best answer is how good you can make the answer. A mediocre answer will be something like completing a project on time. You can say this, but add another twist to make the answer a little better. Here is an example.

This answer is showing that you believe in delivering great quality work. Moreover, it is implying how much you value team work. If you value teamwork highly, then it is safe to assume that you would make a great team player.